L Introduction. 



In the history of plant and animal breeding it has been commonly 

 observed that the mating of different varieties or species may produce 

 offspring which, in certain respects, are unlike either parent. In 

 some instances the qualities of this mixed, or heterozygous, individual 

 are an improvement upon either parent form, just as superior strains 

 of corn are in reahty hybrid-products, or as the crosses between cer- 

 tain varieties of poultry yield birds of different plumage or of larger 

 size than that of either parent. In the continued propagation of these 

 desirable types, the plant or animal breeders have, however, encoun- 

 tered much difficulty. This difficulty deals primarily with the follow- 

 ing circumstance: In the majority of cases the heterozygous form 

 does not breed true ; upon continued propagation it breaks up again 

 into the parent types, and leaves only a certain proportion of heter- 

 ozygous individuals which themselves, when bred further, behave 

 in the same manner.* In other words, no method is known of 

 "fixing" a heterozygous character, — of causing it to faithfully repro- 

 duce itself through successive generations. That knowledge of such 

 a method would be a valuable addition to the theory and practice of 

 both plant and animal breeding, no one can deny; whether it is 

 possible, remains to be ascertained. 



The many variable features possessed by domestic poultry and the 

 ease with which crosses between diverse types can be made, render 

 this group of animals especially favorable for studying the behavior, 

 in inheritance, of such so-called heterozygous characters. At the 

 outset of this investigation, in 1909, barring in fowls was selected as 

 the character to be studied. The barred color-pattern in feathers 

 was then tentatively regarded as a heterozygous condition arising 



*A case in point is that of the Blue Andalusian fowl which is a "hybrid" product and never 

 breeds true. 



